He received his Ph.D. from Stanford in 1993 and has worked extensively on the Wide Area Augmentation System (WAAS). He has received the Thurlow and Kepler awards from the Institute of Navigation (ION). In addition, he is a fellow of the ION and has served as its president.

There has been resurgent interest in building low Earth orbiting (LEO) constellations of satellites on a new scale. Their aim is Internet for the world with plans for potentially thousands of satellites. Here, we explore how these LEO constellations can be utilized for navigation. Closer to Earth, LEO offers stronger signals, strengthening us against jamming and aiding in indoor and urban environments. Proximity is also its weakness, where satellites have a small Earth footprint requiring many to provide global coverage. We show that the strength of the Broadband LEO constellations is their numbers, where they offer threefold improvement in satellite geometry compared to navigation core-constellations today. This allows for relaxation of the signal-in-space user range error, while still matching the position accuracy of GPS. Coupled with the more benign radiation environment in LEO compared to GPS in medium Earth orbit, this enables a navigation payload designed using commercial-off-the-shelf components.

Global Navigation Satellite Systems (GNSS) brought navigation to the masses. Coupled with smartphones, the blue dot in the palm of our hands has forever changed the way we interact with the world. Looking forward, cyber-physical systems such as self-driving cars and aerial mobility are pushing the limits of what localization technologies including GNSS can provide. This autonomous revolution requires a solution that supports safety-critical operation, centimeter positioning, and cybersecurity for millions of users. To meet these demands, we propose a navigation service from Low Earth Orbiting (LEO) satellites which deliver precision in-part through faster motion, higher power signals for added robustness to interference, constellation autonomous integrity monitoring for integrity, and encryption / authentication for resistance to spoofing attacks. This paradigm is enabled by the 'New Space' movement, where highly capable satellites and components are now built on assembly lines and launch costs have decreased by more than tenfold. Such a ubiquitous positioning service enables a consistent and secure standard where trustworthy information can be validated and shared, extending the electronic horizon from sensor line of sight to an entire city. This enables the situational awareness needed for true safe operation to support autonomy at scale.

In this work, the threats to TESLA and the TESLA keychain are evaluated and the weak points in the implementation are identified. Modes of attack are modeled to emulate the effort required for an attacker to break the security of the TESLA keychain. This effort is contextualized with the window of vulnerability which is directly related to the length of the keychain and other variables. The effort required to break TESLA as these variables change is calculated using probabilistic models. While observing the variables' consequences to security, an analysis is carried out that yield recommendations for a secure implementation of the TESLA keychain.

Cryptography in the form of digital signatures can be part of the solution to the threat of spoofing and is going to be implemented on Galileo and other Global Navigation Satellite Systems. Digital signatures incorporated into the data stream authenticate the integrity of the data as well as the origin of the message. Implementing a digital signature on a satellite-based augmentation system for use in aviation will require the signature to be short and the signing procedure to be cryptographically relevant for the next 30 or more years. With the advent of quantum computing, many state-of-the-art authentication schemes are no longer viable, so an authentication scheme implemented in satellite-based augmentation system will need to be quantum secure. This paper introduces the cryptographic primitives (foundational problems) necessary to understand the vulnerabilities in modern-day cryptography due to quantum computing and investigates the use of TESLA (Timed Efficient Stream Loss-tolerant Algorithm) and EC-Schnorr (Elliptic Curve-Schnorr) algorithms in broadcast systems.